sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: tan, grey, brown, white; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8

Hardness: 7 (Mohs scale)
Color: tan, grey, brown, white
Luster: waxy to dull

Identified July 13, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: tan, grey, brown, white; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) on the ocean floor or through chemical precipitation in groundwater replacing limestone. Found in geological formations ranging from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and weapons (knapping); currently used in road construction, as an abrasive, and sometimes in jewelry or decor when polished.

Geological facts

Chert has an extremely sharp edge when broken due to its conchoidal fracture, making it the primary material for prehistoric arrowheads and spear points. It can also produce sparks when struck against steel.

Field identification & locations

Identify by its waxy luster, hardness (can scratch glass), and smooth, curved fracture surfaces. Commonly found as nodules within limestone or chalk beds or as river cobbles.